It is one thing to be poked, high-fived or hugged by your Facebook friends but finding out what they have got you for Christmas is a different matter.

The site's use of Beacon, an advertising system which taps into "word of mouth" marketing, has angered some users by spoiling potential Christmas surprises.

Thousands of Facebook users are protesting against the social networking site's decision to publicise details of their online shopping habits without their permission. The group Facebook: Stop Invading my Privacy is growing by 1,000 members every few minutes, according to users. Its petition reads: "Facebook must respect my privacy. They should not tell my friends what I buy on other sites - or let companies use my name to endorse their products - without my explicit permission."

Facebook users can opt out of having their purchases on sites such as Fandango.com reported to their friends, but critics argue the option is easily missed and must be repeated for every retail site used.

When Facebook launched the service, senior executives said the company would listen closely to what surfers had to say about it.

"Users on Facebook are constantly in there consuming massive amounts of information every day," Owen Van Natta, Facebook's chief revenue officer, said. "We will find out very quickly what people think about things - one of the things about being a technology company, and as an innovator you have to be able to do, is be able to respond very quickly to how people react."

It is not the first time a Facebook feature has been accused of invading privacy. A year ago, a service that let users see what their friends were doing online also faced drew protests.

But after a few controls were added, surfers became used to the idea. The so-called "news feed" feature has now become a central part of Facebook's appeal and has helped propel the site to the point where it has more than 40 million users around the world.

"The thing that we took away from that was that we're a technology company and we build innovation," said Van Natta. "The socialisation of the web is happening at such a rapid pace ... that means a lot of trial and error. We have to do a really good job of communicating with people."